A mixer is a device which converts an incoming from one frequency to another by combining it with a local oscillator signal in a non-linear device. In general, mixing produces a large number of sum and difference frequencies. Usually, the difference frequency between the signal (RF frequency) and local oscillator (LO frequency) is of interest. Mixers are often used in radar systems to convert an incoming RF before further processing.
Monolithic technology has been widely used at lower frequencies (less than 30 GHz) and has proven to be attractive for addressing the problems of cost, size and weight. Those concerned with the development of radars into the millimeter-wave region must often deal with parts which require precise tolerances and are difficult to fabricate. There is a continuing need for low cost radar components with designs amenable to mass production.